304 



CARDIAC MUSCULAR TISSUE. 



CARDIAC MUSCULAR TISSUE. 



The fibres of the heart (figs. 349, 350) differ remarkably from those of in- 

 voluntary muscular organs in general, inasmuch as they present transverse strias. 

 The strise, however, are less strongly marked, and less regular, and the fibres are 

 smaller in diameter than in the voluntary muscles. They differ also from these in 

 being made up of distinct quadrangular cells (fig. 349) joined end to end and often 

 presenting a branched or forked appearance near one extremity (c). Each cell has a 



Fig. 349. Six MUSCULAR FIBRE-CELLS FROM THE HEART, MAGNIFIED 425 DIAMETERS. (E. A. S.) 



a, line of junction between two cells ; b, c, branching of cells. From a drawing by Mr. J. E. 

 Neale. 



Fig. 350. MUSCULAR FIBRES FROM THE HEART, MAGNIFIED, SHOWING THEIR CROSS STHLE, DIVISIONS, 



AND JUNCTIONS. (Schweigger-Seidel.) 



The nuclei and cell-junctions are only represented on the right-hand side of the figure. 



single clear oval nucleus situate near the centre ; occasionally two nuclei are seen* 

 The cell substance is striated longitudinally as well as transversely, its substance 

 appearing to be composed of a number of parallel columns (sarcostyles), which on 

 transverse section are seen as small polygonal areas. An investing membrane or 



Fig. 351. FRAGMENT OF THE NET- 

 WORK OF PURKIBJE FROM THE 

 VENTRICULAR ENDOCARDIUM 01* 



THE SHEEP. (Ranvier.) 3 2. 



c, cell ; /, striated substance ', 

 n, nuclei. 



sarcolemnia has not hitherto 

 been proved to exist on these 

 fibres. 



The muscular fibres of the 

 heart freely divide and anas- 

 tomose (fig. 350), the junc- 

 tions with neighbouring fibres being effected by the medium of the cell-offsets 

 above noticed. 



In the frog and lower vertebrate generally the muscular fibres of the heart are 

 formed of elongated spindle-shaped cells, resembling in shape the cells of plain mus- 

 cular tissue, but exhibiting distinct transverse striation. 



